PocketLocker creates scalable, reliable, and performant personal storage clouds out of available space distributed across multiple personal devices. Designed to store rarely-changed files on both interactive devices with limited storage (such as smartphones) and non-interactive devices with large amounts of storage (such as storage appliances), PocketLocker differs from previous systems in not requiring that each device be able to store all available content or be configured to only view certain files. Instead, a storage orchestrator running as a cloud service distributes erasure-coded file chunks across all available devices to maximize performance and capacity and minimize energy usage at battery-powered clients while meeting configurable backup requirements. Unlike current cloud storage options, PocketLocker is free and will scale as users add devices. We motivate PocketLocker's design by analyzing two months of file access traces taken from 100 smartphones, and evaluate its performance using trace-based simulations to explore design parameters and measurements of a prototype Android implementation to establish real-world performance. By locating content close to where it will be accessed by mobile devices, PocketLocker provides low-latency access to large amounts of content. By exploiting mobility and charging habits, PocketLocker can meet backup requirements without draining the smartphone's battery.